Some eco - Physiological responses of Mail Nileand ilapia [Oreochromis Niloticus] to thermal and salinity conditions

ABSTRACT

Two trials were conducted in Animal Physiology Lab., Faculty of Agriculture; Cairo University from May to November, 1999 to quantify and evaluate the growth performance of male Nile Tilapia [Oreochromis niloticus] affected by physiological responses to thermal and salinity conditions in aquaria. The experiments were conducted cither on fry [for 30 days] or fingerlings [for 42 days]. The experimental study incorporated six treatments [T1-T6] between two temperature degrees [28.59, 33°C for fry mid 23.91, 33°C for fingerlings] and three salinity levels fresh brackish and sea water [0.1, 15 and 30 ppt, respectively]. Both dissolved oxygen [DO] and pH did not reach critical values for both fry and fingerlings. The daily weight gain of fry was greater [0.145 g/ fish/day] in fresh water than in brackish water [0.041 g/fish/ day]. The lowest daily gain was in seawater [0.037 g/fish/day], the differences were significant [p < 0.05]. After 30 days from starting the experiment, the daily weight gain of finger-lings showed equal means [0.1955 and 0.196 g/ fish/day] in both fresh water and brackish water, compared to half value in seawater [0.096 g/fish/ day]. The fish could not tolerate the high temperature and/or concentrated salinity [seawater 30 ppt] further than 30 days. It was obvious that the fish chemical constitutions were not affected by temperature or salinity us well as their interactions. The concentrations of Na[+], K[+], P[---] and Cl- in blood plasma were, 477 47, 40.44, 0.88 and 249.09 mg/dl, respectively, under fresh water [0.1 ppt salinity]. In the sea water [30 ppt salinity] the values were 490.97, 34.37, 1.24 and 300.5 mg/dl, while in brackish water were 456.45, 31.99, 1.31 and 337.59, respectively. The ions [Na[+], K[+] and P[---]] besides Ca[++] and Mg[++] in the fish tissue [dried body] were 22.95, 0.21, 3.36, 41.18 and 2.27 mg/g respectively in fresh water [0.1 ppt], while in seawater [30 ppt] the values were 18.1, 0.19, 3.38, 42.09 and 2.31 mg/g respectively. Fish in seawater treatments had the highest concentration of aldosterone hormone in blood plasma with the average of 0.55 picag/ml, while fresh and brackish water treatments induced lower and similar concentrations of aldosterone, 0.46 and 0.48 picog/ml, respectively after 30 days